1. Field of the Invention
The present invention relates to data converting, and more particularly, to a data converting device for improving image quality, a method thereof, and a liquid crystal display (LCD) device having the same.
2. Description of the Related Art
Cathode ray tubes (CRTs) have disadvantages of being heavy in weight and having a large volume. Flat panel display devices are under active development in order to overcome these disadvantages of the CRTS. The flat panel display devices include LCD devices, field emission display (FED) devices, plasma display panels (PDPs), and electro-luminescence (EL) display devices. The flat panel display devices displays an image corresponding to image signals (e.g., television image signals) received from the outside. These flat panel display devices include a panel for displaying the image corresponding to the image signals, and a driving unit for driving the panel.
The image signals are roughly classified into progressive type signals and interlace type signals depending on a displaying method.
In a progressive type displaying method, an image is displayed by image signals constituting one screen, that is, by one frame unit. Representative examples of progressive type flat panel display devices include computer monitors, PDPs, and LCD devices. Therefore, the LCD devices display image signals in a frame unit.
In an interlace type displaying method, image signals constituting one screen, that is, one frame, are divided into an odd field displaying odd horizontal lines and an even field displaying even horizontal lines. Image signals are supplied in order of the odd field and the even field to display one corresponding frame. Representative examples of these interlace type display devices include television (TV) sets. The TV sets receive interlace type image signals for a TV from a broadcasting station and directly display the interlace type image signals for the TV using the interlace type displaying method.
A broadcasting station transmits interlace type image signals for a TV. Therefore, in the case where the LCD device is used in a TV set, interlace type image signals for the TV cannot be directly displayed on the LCD device because the LCD device processes a predetermined image using the progressive displaying method.
The LCD device includes a liquid crystal (LC) panel in which a plurality of pixels displaying an image are arranged in a matrix, and a driving unit for driving the LC panel.
The LC panel includes a plurality of horizontal lines and a plurality of vertical lines. The pixels are defined by the horizontal lines and the vertical lines. Pixel electrodes are formed on the pixels, respectively. Also, red (R), green (G), and blue (B) color filters are formed on regions corresponding to the pixels.
The driving unit includes a gate driver for sequentially supplying scan signals to the horizontal lines, a data driver for a predetermined image signal to the vertical lines, and a timing controller for generating control signals for controlling the gate driver and the data driver.
The horizontal lines are sequentially driven by scan signals supplied by the gate driver. An image signal supplied from the data driver is applied to the pixels via the vertical lines, so that a predetermine image is displayed using the color filters. That is, image signals of one frame are displayed in response to the sequentially drive horizontal lines.
Therefore, the progressive displaying method is suitable for an LCD device where the horizontal lines are sequentially driven. In other words, since the horizontal lines are sequentially driven regardless of odd horizontal lines and even horizontal lines in the LCD device, the progressive displaying method is suitable.
In the case where the LCD device is used for a TV set, interlace type image signals are provided from a broadcasting station. Accordingly, it is not easy to display the interlace type image signals using a progressive type LCD device.
To solve this problem, a method for displaying interlace type image signals using an LCD device without converting the interlace type image signals into progressive type image signals has been proposed.
In detail, interlace type image signals where an odd field and an even field are repeated are supplied to an LCD device. In the odd field, actual pixel data exists only on odd horizontal lines, and does not exist on even horizontal lines. On the other hand, in the even field, actual pixel data exist only on even horizontal lines and does not exist on odd horizontal lines. Therefore, a complete one frame includes the odd field and the even field.
When an odd field is supplied, the LCD device generates dummy pixel data on the even horizontal lines using actual pixel data existing on adjacent odd horizontal lines. Accordingly, since actual pixel data exists on the odd horizontal lines in the odd field and the dummy pixel data exists also on the even horizontal lines, the odd field itself can constitute a complete one frame. Also, when an even field is supplied, the LCD device generates dummy pixel data on the odd horizontal lines using actual pixel data existing on adjacent even horizontal lines. Accordingly, since dummy pixel data exists on the odd horizontal lines in the even field and actual pixel data exists on the even horizontal lines, the even field can constitute a complete one frame. A variety of methods for generating the dummy pixel data exist. The dummy pixel data is at least smaller than the actual pixel data. Therefore, each of an odd field and an even field can be regarded as one frame. Each of the odd field and the even field will be treated as a frame in the following description.
The LCD device sequentially drives respective horizontal lines during a first frame to display pixel data in an odd field, and sequentially drives respective horizontal lines during a second frame to display pixel data in an even field. Therefore, the LCD device can directly display interlace type image signals containing the odd field and the even field.
FIG. 1A is a view illustrating pixel data in an odd field supplied using an interlace type is displayed on a liquid crystal (LC) panel, and FIG. 1B is a view illustrating pixel data in an even field supplied using an interlace type is displayed on an LC panel.
Referring to FIG. 1A, in case of an odd field, actual pixel data can be displayed on odd horizontal lines, and dummy pixel data can be display on even horizontal lines.
Referring to FIG. 1B, in case of an even field, dummy pixel data can be displayed on odd horizontal lines, and actual pixel data can be displayed on even horizontal lines.
Referring to FIG. 2, interlace type image signals are inverted and dot-inverted by a field unit in order to improve display quality.
In detail, in interlace type image signals, an odd field period and an even field period are repeated, so that an odd field and an even field are displayed. It should be noted that each of the odd field period and the even field period corresponds to one frame period.
Referring to FIG. 3, a predetermined pixel on odd horizontal lines is charged with actual pixel data of positive polarity (+) with respect to a common voltage Vcom during a first odd field (OF) period. The predetermined pixel is charged with dummy pixel data of negative polarity (−) during a first even field (EF) period. Subsequently, the predetermined pixel is charged with actual pixel data of positive polarity (+) during a second odd field (OF) period. Also, the predetermined pixel is charged with dummy pixel data of negative polarity (−) during a second even field (EF) period. In this manner, the predetermined pixels are charged with actual pixel data and dummy pixel data in turns by a field unit. As described above, since the dummy pixel data is calculated using actual pixel data on adjacent horizontal lines, an absolute value of the actual pixel data is far greater than that of the dummy pixel data. Accordingly, voltages that charge pixels on the odd horizontal lines and pixels on the even horizontal lines have an average voltage (DC voltage) of positive polarity (+) with respect to the common voltage Vcom as the odd field period and the even field period repeat. A DC voltage having positive polarity (+) is applied to the pixel, resulting in a serious afterimage.
To solve this problem, polarity of pixel data is inverted by a two-field unit (an odd field and an even field) as illustrated in FIG. 4.
In detail, referring to FIG. 5, predetermined pixels on odd horizontal lines are charged with actual pixel data of positive polarity (+) with respect to the common voltage Vcom during a first odd field period. The predetermined pixels are charged with dummy pixel data of positive polarity (+) during a first even field period. The predetermined pixels are charged with actual pixel data of negative polarity (−) during a second odd field period. The predetermined pixels are charged with dummy pixel data of negative polarity (−) during a second even field period. Polarity of pixel data is inverted by a two-field unit in this manner.
In this case, actual pixel data of positive polarity (+) charged during the first odd field period and dummy pixel data of positive polarity (+) charged during the first even field period, and actual pixel data of negative polarity (−) charged during the second odd field period and dummy pixel data of negative polarity (−) charged during the second even field period, are symmetric with respect to the common voltage Vcom, these data cancel each other to become a zero average value (DC voltage). Therefore, a DC voltage is not applied to the pixel and thus an afterimage is not generated.
However, although an afterimage is prevented by inverting polarity of pixel data by a two-field unit, flicker may be constantly generated. That is, referring to FIG. 6, predetermined pixels on the horizontal lines are charged with actual pixel data of positive polarity (+) during a first odd field period. Subsequently, the predetermined pixels are charged with dummy pixel data of positive polarity (+) during a first even field period. In this case, since all of the pixel data have the same polarity of (+) during the first odd field period and the first even field period, all of the pixels charged with the actual pixel data during the first odd field period are not discharged, but rather a portion of a DC voltage remains. Therefore, the residual DC voltage during the first odd field period is added to the dummy pixel data of the first even field period, so that the pixel is charged with dummy pixel data greater than the dumpy pixel data during the first even field period. The above process is repeated every even field period. Therefore, since a desired image is not displayed during an even field period under influence of a residual DC voltage in an odd field period, flicker is generated. This flicker is particularly serious in the case where pixel data of the same brightness is displayed by each field unit. For example, in the case where both a first odd field and a first even field are white, a pixel data value in the first even field increases due to a DC voltage existing on horizontal lines of the first odd field. Accordingly, not only is the same white not realized on the first odd field and the first even field, but also serious flicker is generated.